Batch processing to remove unwanted parent tags?

[Info Munky]

Digikam 4.12.0 on Linux Mint 18 Cinnamon

I'm considering moving from Shotwell (the simplicity of which I like) to 
Digikam, primarily because Shotwell doesn't easily allow me to 
dissociate RAW files from JPGs after import. I've been experimenting 
with Digikam, getting to grips with it and starting to really love it!

Main issue I need to resolve at the moment is how to remove parent tags 
(in my JPG metadata from Shotwell) where I have a child or children of 
that parent tag.

If my tag hierarchy is something like this...

a
     aa
     ab
     ac
         aca
b
     ba

... and photo 1 has tag 'aca' set, I currently have tags 'a', 'ac' and 
'aca' showing against the photo either in the tool tip or under the 
thumbnail. I have seen that after removing 'a' and 'ac', the photo still 
shows up in a search for either of these tags, because 'aca' is a 
descendent. So I'd like to remove 'a' and 'ac' from photo 1 to remove 
clutter when the tags are listed.

Obviously I can remove these one by one, but am wondering whether 
there's a nice script somewhere to do this on a batch basis?

Thanks